Fabrics obtained by weaving, as warps and wefts, monofilaments made of a synthetic resin have conventionally been used widely as an industrial fabric. They are, for example, used in various fields including papermaking fabrics, filter cloths and conveyor belts and are required to have fabric properties suited for the intended use or using environment. Of these fabrics, a papermaking fabric used in a papermaking step such as removal of water from raw materials by making use of the network of the fabric must satisfy severe requirements. There is therefore a demand for the development of fabrics which are equipped with fabric rigidity such as diagonal rigidity and flexural rigidity, dimensional stability and wear resistance high enough to permit preferable use under severe environments; and can maintain conditions necessary for making good paper for a prolonged period of time. In addition, surface property, fiber supporting property, improvement in a papermaking yield, good water drainage property and running stability are required. In recent years, owing to the speed-up of a papermaking machine, requirements for papermaking wires become severe further.
Since most of the demands for industrial fabrics and solutions thereof can be understood if papermaking fabrics on which the most severe demand is imposed among industrial fabrics will be described, the present invention will hereinafter be described by using a papermaking fabric as a representative example.
Physical properties which a papermaking fabric must have include rigidity, dimensional stability, wear resistance, surface property, fiber supporting property, improved yield of raw materials for paper manufacture, good water drainage property and running stability. A variety of studies on the fabric design, quality of yarns and weaving conditions and trial production based on such studies have been performed in order to satisfy such requirements. Among factors having a great influence on the physical properties of a fabric, yarns constituting a fabric are important so that researchers have carried out an extensive investigation on their main components, additives, mixing ratio, and characteristics of yarns.
In Japanese Patent Laid-Open Publication No. 2000-144531, disclosed is a polyamide monofilament excellent in wear resistance and heat set property and an industrial cloth which is obtained using the polyamide monofilament and is capable of retaining the woven surface stably with firm knuckle portions. This invention relates to a monofilament obtained by copolymerizing two polyamides. It has characteristics in its components, mixing ratio, concentration of an amide group and melt viscosity.
The polyamide monofilament disclosed in the above-described invention has a wet/dry tensile strength ratio of 85% or greater, a wet/dry flexural rigidity ratio of 55% or greater, maximum longitudinal dimensional change of 4% or less due to moisture absorption or desorption, and a heat set tension ratio, as expressed by a ratio of a yarn tension at normal temperature to a yarn tension prior to heat treatment when the monofilament is heat set at a temperature of from 100° C. to the melting point under tension and then cooled as is, of 2 times or greater. According to this document, the polyamide monofilament therefore does not lose excellent characteristics of polyamide such as wear resistance, has only a small difference in the characteristics between dry time and wet time, can undergo thermal correction easily even in a fiber state because of excellent heat set property, and maintain a stable woven surface because a firm knuckle portion prevents misalignment of constituent yarns during use. The above-described values of the physical properties of this polyamide monofilament such as wet/dry tensile strength ratio, wet/dry flexural rigidity ratio, the maximum longitudinal dimensional change due to moisture absorption or desorption, and heat set tension ratio are however not special but similar to those of conventional polyamide monofilaments or copolymerized polyamide monofilaments. In particular, it is known that Nylon 6 also shows a heat set tension ratio of two times or greater, and it has the maximum dimensional change of 4% or less. Moreover, even if the monofilament has a high wet/dry rigidity and improved heat set tension ratio, it does not mean that an industrial fabric obtained using it has a firm knuckle portion and becomes stable without misalignment of constituent yarns upon use.
Thus, even if the polyamide monofilament has such a novel constitution, fabrics obtained by weaving it are not worth using as an industrial fabric when they cannot have physical properties suited for the intended industrial fabric. Moreover, it is difficult for the fabric as disclosed by the above-described patent document to satisfy the properties required for an industrial fabric such as fabric rigidity such as diagonal rigidity and flexural rigidity, dimensional stability, wear resistance, surface property and running stability.
An object of the present invention is to provide an industrial fabric excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, weaving strength, dimensional stability, running stability, fibrillation resistance, wear resistance, resistance to moist heat, heat resistance, and chemical resistance and is stable without causing misalignment of constituent yarns: and a constituent yarn of the fabric.
In the present invention, a polyamide obtained by polycondensation reaction between metaxylenediamine and adipic acid is called “Polyamide (A)”, while another polyamide is called “Polyamide (B)”. A yarn composed of a polyamide obtained by mixing from 5 to 50 wt. % of Polyamide (A) with from 95 to 50 wt. % of Polyamide (B) is called “polyamide filament (M)”.
The present invention relates to a polyamide filament used for an industrial fabric, which comprises a polyamide resin composition obtained by mixing from 5 to 50 wt. % of a crystalline polyamide (A) obtained by polycondensation reaction of metaxylenediamine and adipic acid and from 95 to 50 wt. % of another polyamide (B). After heating (to 160 to 200° C.) under a constant length condition (at an initial load of 20 mg/d), the filament does not reduce a thermal contraction stress thereof in a cool-down region not greater than 80° C. The polyamide filament may be a monofilament or multifilament. The polyamide (B) may be any one of Polyamide 6, Polyamide 66, Polyamide 610, Polyamide 612 and a polyamide copolymer or a mixture of two or more thereof. From 20 to 40 wt. % of the crystalline polyamide (A) may be mixed with from 80 to 60 wt. % of the another polyamide (B). The polyamide filament as described above may be used as at least a portion of wefts and warps of an industrial fabric.
The present invention relates to a polyamide filament obtained by mixing predetermined amounts of specified two polyamides and does not reduce its thermal contraction stress by cooling to room temperature after heating; and an industrial fabric using this filament as a constituent yarn of the fabric. This fabric is excellent in fabric rigidity such as diagonal rigidity and flexural rigidity, weaving strength, dimensional stability, running stability, fibrillation resistance, wear resistance, resistance to moist heat, heat resistance, and chemical resistance and is stable without causing misalignment of constituent yarns; and is suited for papermaking fabric, filter cloth of a dehydrator or conveyer belt.